The subject disclosure relates to flash memory devices, such as solid-state drives (SSDs), that use flash memory to store data.
Over time, the cells of a flash memory device lose charge, which can cause the threshold voltage of flash memory cells to drop. The more program/erase cycles the device has experienced, the more extreme the decline in the threshold voltage. As the threshold voltage values drop in multi-level cell (MLC) flash memory, some of the cells programmed to the first level may fall below zero. Because read levels cannot be placed below zero, these programmed cells can be harder to decode. Eventually, errors originating from programmed cells that have drifted below zero volts can dominate the overall error rate of the device.